Various attempts have heretofore been made to supply liquid fuel in atomized form into a combustion or precombustion chamber of an internal combustion engine such as diesel or gasoline engine in order to reduce soot and enhance fuel economy. One of the most common methods is to inject liquid fuel under pressure through the outlet port of an injection nozzle. In such injection it is known that atomization of liquid fuel is promoted by imparting ultrasonic vibrations to the liquid fuel.
There have heretofore been developed two mechanisms for atomizing liquid by ultrasonic waves--(1) the cavitation mechanism and (2) the wave mechanism. The cavitation mechanism is unsuitable for application to an injection valve because of difficulty in controlling the degree of atomizing. The wave mechanism includes the capillary system and the liquid film system. In the capillary system an ultrasonic vibrating element has a capillary aperture formed therethrough. Liquid fuel is introduced through the inlet port of the capillary aperture while the ultrasonic vibrating element is subjected to vibration, whereby the liquid fuel is spread through the outlet of the capillary aperture in a film form over the bottom surface of the vibrating element and then injected in an atomized state, In the liquid film system, an ultrasonic vibrating element is formed on its forward end with a portion flared as in the form of a poppet valve. Liquid fuel is delivered to and spread over the face portion in a film form and then injected in an atomized state.
As is understood from the foregoing, it has been heretofore considered that the mechanism by which liquid is atomized by means of an ultrasonic vibrating element is based on either cavitation or wave motions caused after the liquid is transformed to film, and particularly that wave motions in film are indispensably required to effect atomization of liquid in a large quantity. Accordingly, the arrangements as describcd above have been hitherto proposed.
However, in actuality the injection nozzles hitherto proposed have such small capacity for spraying that they are unsuitable for use as an injection nozzle for internal combustion engines such as diesel or gasoline engines which require a large amount of atomized fuel.
In an attempt to accomplish atomization of liquid fuel in a large quantity, the inventors of this application have conducted extensive research and experiments on the mechanism by which liquid is ultrasonically atomized as well as on the configuration of the ultrasonic vibrating element and found out that it is possible to effect atomization of liquid fuel by an atomization mechanism distinct from the atomization mechanisms as described hereinabove. More specifically, the inventors have discovered that liquid fuel may be atomized in a large quantity from an edged portion formed at an end of an ultrasonic vibrating element by delivering liquid fuel to and past said edged portion in a film state. This invention has been developed on the basis of such novel discovery.